A new NBC-Marist poll confirms that with the caucuses four days away former Massachusetts governor Mitt Romney is the frontrunner in Iowa (with Texas Rep. Ron Paul close on his heels), while former Pennsylvania senator Rick Santorum is experiencing a late-in-the-game surge.

Romney and Paul are battling for the top spot, winning the loyalty of 23 percent and 21 percent of likely caucus-goers, respectively. The survey finds Santorum at 15 percent, a jump from 6 percent over the last month. The caucuses are Jan. 3.

At the beginning of the month in this NBC/Marist series, Romney and Paul tied at 19, while Santorum languished at 6% among likely voters. Both sets of numbers included leaners, which only dropped the undecided respondents from 12% to 7%, and boosted Ron Paul more than anyone else (two points to one for both Romney and Santorum). Newt Gingrich has seen his support drop by more than half in the same period, from 28% to 13%, while Rick Perry rose from 10% to 14% to finish just behind Santorum. Michele Bachmann lost a point this month, essentially treading water near the bottom of the pack.

In the second-choice category, Perry finished second to Romney, 21/20, with Santorum in third at 15%. That’s almost double what both Perry and Santorum had at the beginning of the month, but Romney’s second-choice support has grown, too. Most of that came from Herman Cain’s former second-choice support as well as a significant decline for Gingrich, who at 13% still has an edge over Paul’s 9%. That figure seems to indicate that Paul’s support in the caucuses is shallow indeed; he’s gotten all of the support he can muster at this point. Any late breaking decisions by voters will favor Romney, Perry, and Santorum most as voters move away from other candidates.

I think it’s safe to say that NBC/Marist and Rasmussen have a good handle on what the race in Iowa looks like this week. We’ll see what Iowans think by Tuesday. One key Iowan still hasn’t made up his mind, but has begun to say what he can abide, at least — and what he can’t:

Steve King would be warmly welcomed onto any of the campaign buses crisscrossing Iowa in the homestretch before Tuesday’s caucuses, but he spent Thursday at his home in the state’s conservative northwest.

The influential congressman’s position on the sidelines epitomizes the failure of Iowa’s abundant social conservatives to unite behind one candidate who could overtake Mitt Romney, widely distrusted because of his Mormonism and previous support for abortion and gay rights. King expected to settle on a candidate in September or October. He didn’t. …

Erick Erickson, the popular conservative blogger for RedState, mocked Santorum’s rise to third place in the poll, noting the former Pennsylvania senator’s threadbare campaign outside of Iowa. That’s was Mike Huckabee’s problem after Iowa’s social conservatives put him over the top in the 2008 caucuses. “No Surprise, Iowa Social Conservatives Are About to Shoot Us All in the Foot Again,” read the headline on Erickson’s post about the new poll. A Santorum surge, Erickson wrote, means Romney is likely to win the nomination.

That prospect doesn’t bother King, who pointed to Romney’s “exemplary family life” with his wife of 42 years and five sons. “He has more children and fewer vices than I have, so how can I criticize him?” King said, in what could be viewed as an appeal to social conservatives to come to terms with Romney’s likely success. “I could do business with Mitt Romney. I could do business with any of these candidates.”

Actually, there is one candidate whose foreign policy position troubles King far more than Romney’s waffling on abortion. Ron Paul advocates pulling all American troops out of foreign countries as part of a massive military disengagement. “That would be a calamity,” King said. He also worries that a Paul victory in the Iowa caucuses would diminish the state’s status because the quirky libertarian is so unlikely to win the nomination.

I don’t think I ever got a chance to post an interview I conducted with Rep. King before the debate in Des Moines on December 10th, so now seems like a good time to do so. King clearly wants to find a candidate he feels comfortable in endorsing, and his endorsement is probably the one left on the table that could still make some difference, but just as was three weeks ago, King still hasn’t found the right fit.